Perl call a sub routine that exists inside of an array - perl

Question

I am trying to make a state machine in Perl. To do this I have an array indexed by statenames. I can put subs into this array. Like this:
use constant {
stInit => 0,
stHeader => 1,
stSalesHeader => 2,
stCatagory => 3,
stData => 4,
stTotal => 5,
stError => 6,
};
my $state = stInit;
my #actions;
$actions[stInit] = [sub{logState("Initial state entered",2) }];
$actions[stHeader] = [sub{logState("Header state entered",2) }];
$actions[stSalesHeader] = [sub{logState("Sales header state entered",2) }];
$actions[stCatagory] = [sub{logState("Category state entered",2) }];
$actions[stData] = [sub{logState("Data state entered",2) }];
$actions[stTotal] = [sub{logState("Total state entered",2) }];
But then I have no Idea how to call the subroutine. I have tried this
$actions[$state]
But that appears not to work. Is this possible or am I completely off?

Answer 1

You really should add
use strict;
use warnings;
to the start of your code, which will find many simple mistakes for you. In this case your code is fine, and you can call your subroutines by using
$actions[$state][0]();
etc.
But there is no need to put the subroutines within square brackets, which just creates a one-element anonymous array and adds an additional level of indexing (hence the [0] in the above line of code. If you wrote code like this instead
$actions[stInit] = sub { logState("Initial state entered", 2) };
then you would be able to call the subroutines with
$actions[$state]();

Answer 2

On an a slightly different note, have you considered using FSA::Rules to write your state machine? It's fairly powerful, has optional GraphViz output and makes state machines rather easy to write.

Answer 3

You should do:
&{$actions[$state][0]}
but I'm not sure why you use an array... If you have just 1 function then
$actions[stData] = sub{ ... }
...
&{$actions[$state]}
will work. If you really want to execute many functions and use the array, then you can do:
map { &{$_} } #{$actions[$state]};

Answer 4

To call a subroutine from a reference:
&{$actions[$state]}();
However, based on your code, #actions does not contain subroutine references, but array references to the declaration of the subroutine.
first, declare the subs as you normally would and then build #actions:
$actions[0] = \&stInit;
$actions[1] = \&stHeader;
...and so on

Answer 5

Drop the extraneous anonymous array creation by removing the square brackets
$actions[stInit] = sub{logState("Initial state entered",2) };
You can then call the action with
$actions[stInit]();
If you have an action stored in a variable, e.g.
my $action = $actions[$actionID];
then you'll need a bit more syntax to make it actually do the call
$action->();
Then again, you could just use a hash instead of an array
my %actions = (
stInit => sub { logState("Initial state entered",2) },
stHeader => sub { logState("Header state entered",2) },
stSalesHeader => sub { logState("Sales header state entered",2) },
stCatagory => sub { logState("Category state entered",2) },
stData => sub { logState("Data state entered",2) },
);
which would save you from having to set up constants at the top. You could then call actions with
$actions{$state}();